The oligosaccharides are a new generation of functional food or health food ingredient with special physiological effects which can promote the proliferation of colonic Liacteria of genus Bifidobacterium to balance the microbial ecology of the microflora in gastrointestinal tract of human being, suppress the growth of undesirable bacteria and function as an anti-dental caries. Oligosaccharides are a type of sweetener that is not absorbed or digested in the small intestine of man. Oligosaccharides are low in calories and can be used as conventional diet sweeteners such as those used by middle-age and older people who are on special diets due to diabetes.
Oligosaccharides are carbohydrates consisting of 3 to 5 monosaccharides linked together. There are two main methods to produce oligosaccharides. One method involves the application of retrosynthetic reaction of amylase with which the monosaccharides (glucose) are condensed to oligosaccharides. Normally the content of G3 to G5 in the final product is 20%-30% with some other complicated components. G3 and G5 refer to Glucose units. By way of example, G3 refers to a sugar which is comprised of three glucose units linked together as one component.
The other way to make oligosaccharides is the enzymatic hydrolysis method in which the starch is hydrolyzed to polysaccharides first by α-amylases, and then the polysaccharides are further hydrolyzed to oligosaccharides by glucosidase or other enzymes with transglucosylation function. Currently, the enzymatic hydrolysis method is the main process. It is based on starch as raw material. The process comprises two steps. The first step is to get the maltose syrup through starch hydrolysis with α-amylases. The second step is to get the target product through transglucosylation with the co-reaction of two or three kinds of enzymes, and then the routine filtration, decolouration, desalting and concentration processes are applied to get the final product.
Currently, the normal content of oligosaccharides is about 50%-60%. The other main components are glucose and maltose which make about 50% of the final product. The glucose and maltose can disturb the two main health benefits of oligosaccharides product. One is the proliferation of beneficial microbiota Bifidobacteria species in the gastrointestinal tract of humans, and the other is the anti-dental caries benefit. As a result, the health benefits and commercial value of the oligosaccharides product are significantly reduced.
Normally, oligosaccharides with high purity can be obtained by a separation process from the raw oligosaccharides product.
One of separation methods is the membrane separation process. The membrane separation process removes the monosaccharides and disaccharide from the product and keeps the other sugars components with bigger molecular weights, so that the content of oligosaccharides is increased to about 80%. There are problems with this process including the high cost of expensive equipment, low efficiency and difficulties in commercial production.
The other method is the adsorption separation process. The absorption separation process involves removing the monosaccharide and disaccharide by ion exchange columns. The content of oligosaccharides can be increased to 60%-70% by one recycle operation. The disadvantage of this method is that capacity of the columns is low for the single recycle so that multiple recycle adsorption processes are needed to get the high purity oligosaccharides product.